taylor and f



W. TAYLOR AND F. W. PRESTON. I METHOD FOR PREPARING LENSES AND THE LIKE FOR GRINDING AND POLISHING.

APPLICATION FILED AUG. I8, I920.

1 ,35S-,676, Patented Nov. 9, 1920.

f 2 'SHEETS-SHEET I.

,Mw j.

E; mom/fr W. TAYLOR AND F. W. PRESTON. VMETHOD FOR PREPARING LENSES AND THE LIKE FDH GRINDING'AND POLISHING.

APPLICATION FILED AUG. I8: i920.

Patented N ov. 9, 192ml 2 SHEETS-SHEET 2.

QM 3 had; mdf/mmm Zan fr0/mfr nasac'rc.

narran STATES PATENT OFFICE. Y

WILLIAM TAYLOR AND FRANCIS WILLIAM PRESTON, OF LEICESTER, ENGLAND.

METHOD FR PREPABING LENSES AND THE LIKE FOR GRINDING- AND POLISHING.

Specification of Letters Patent.

Application filed August 18, 1920. Serial No. 404,450.

To all 'u1/7mm f/ may conce? lie it known that We, llrnnniir TAYLOR, a resident of Leicester, in the county of Leicester, England, a subject of the King of Great Britain, and llnaNcIs WILLIAM PRES- 'rom a resident of Leicester', in the county of Leicester, England, a subject of the King of Great Britain, have invented certain new and useful Improvements in Methods for llreparing Lenses and the like for Grinding and Polishing, of which the following is a specifica-tion.

rlhs invention relates to improved methods for mounting lenses and the like in preparation for grinding and polishing operations, and is particularly directed to methods of conditioning the binder by means of which the lenses are mounted.

This application is a continuation in part of our previous application Serial No. 357,865, tiled February 11, 1920.

ln the production of lenses and like objects (all of which will hereinafter be referred to as lenses having a surface or surfaces requiring grinding and polishing, it is usual. during the grinding and polishing operations, to protect the rear surface ofthe lens by means of an adherent mass ot cementitious or binding material which on the one hand, if a lens is to be Worked singly, may be made to serve as a holder' or handle, and which on the other hand, if the lenses are to be manufactured in quantity, will enable a number of lenses to be assembled and attached to a single rigid holder se as to form a block such that all the lenses of the block can be ground and polished together.

The cementitious or binding material employed may be a compound capable of being softened by heat, and in such case usually comprises a bituminous substance and a stifening agent. Of these, the bituminous substance may be coal-tar pitch, Wood-pitch, natural bitumen of suitable quality, or any similar substance or mixture (all of Which.

are hereinafter referred to as pitch While the stilfening agent, Which is incorporated with. the pitch, may consist of linely-divided mineral matter such as Woodash, yelloiveocher, or other substance Which,

in addition to stifening the mixture, Vis adapted to reduce the thermal `expansion of the mass and capable (if of suitable character for such purpose) of increasing its thermal conductivity. A'composition which has beenV found satisfactory in practice comprises the following Vproportions by Weightt Coal-tar pitch Qparts. Nood ash 1 part.

Such a compound of pitch and a stifening agent will be referred to hereinafter as a binderf but it should be understood that by the use of this term We do not intend to limit ourselves to a binder of the particular composition which has been stated by Way of example.

Investigation has shown us that' the binder thus constituted should possess the property of being, at ordinary temperatures, what may be termed self-annealing, by which term is meant the property by reason of which the stresses set up in the mass of binder during cooling and shrinking become relieved Within a comparatively short space of time` after the binder has set. lllhen this property exists, it is found that although, after being applied to a lens, the binder cools and shrinks so to produce in the lens a distortion which may continue for some minutes, yet Within (say) half an hour the strain is relieved and the lens becomes free from distortion, This desideratum may be fulfilled by the binder in its initial state, but ive have ascertained by means of polariscopic tests that, with the method of treatment hitherto followed, the self-annealing property has not been maintained for any length of time. That is to say, heretofore, it has been the usual prac tice to keep the binder melted in open Vessels (commonly known as pitch-pots at a general `temperatin'e of about 110 to 120 degrecs centigrade; under which conditions there is sloivly driven-off a mixture of vola tile oils so that the binder gradually detericrates and becomes harder, losing its self annealing property. rlhis deterioration is aggravated by heating the pot With a gas llame in such a Way that the temperature of the binder may locally exceed, by aconsiderable amount, the temperature just named. In consequence of this deterioraw tion, the lenses to which the binder is applied not only become distorted as the binder` .cools and shrinks upon them, but remain Patented Nov. 9, 1920.

final` accuracy of the lenses is seriously affected. Frequent disturbance, or rupturing of the surface, of the molten binder in the pitch-pot by stirring, accelerates the deterioration.

Investigation has shown us that, concurrently with the loss of volatile oils, there occurs a gain in weight which compensates to some extent the loss of weight due l,to the yolatilization of the oils and which probably represents the effect oi oxidation consequent on exposure to the atmosphere. The changes thus produced are irreversible; and although'the binder may be re-softened by the addition of green (anthracene) oil, it does not, after such re-sotening, exhibit its original qualities.

According to the present invention the binder, constituted as above described and preferably having a content of stiiiening agent as high as is compatible with retention et the above-mentioned self-annealing quality, as for example, agcontent'ot stitfening agent amounting to". one-halt the content or pitch by weight is, during use, kept melted in a'closed vessel at a temperature which doesnot materially-exceed that at which destructive change occurs in the composition of the binder; the molten binder being' preferably stirred continuously (without exposing it to contact with the atmosphere) in such manner that uniform distribution of the heat is promoted and segregation of the constituents of the binder is prevented. For this purpose the closed vessel may be provided with a steam-jacket (or other heating device) and means for supplying thereto steam (or other heating agent) at a suitable temperature, a mechanical stirring-device and means for continuously actuating the same, and a gate-centrolled outlet which may also be steam-V jacketed (or otherwise heated) so as to insure the maintenance of fluidity up to the point of discharge of the. binder from the vessel. Y

The temperature within the closed vessel should be'ra-ised only' so tar (to about 130 or lllO degrees centrigrade) as to insure in the binder such fluidity as is necessary for enabling it to be poured and molded with facility; this temperature, while somewhat higherY than. that usually employed with an open pitch-pot, being not too high when used with a closed vessel wherein the risk of deterioration (owing either to volatilization of the oils or the presence oi traces of atmospheric air) is minimized, and being moreover sufficiently low both to obviate injury to the lenses to whichthe binder is applied, and also to expedite the subse quent cooling of; such` lensesv to ordinary room-temperature; A Y

WeLhave found that the binder, prepared asdescri-bed, is capable otretaining its seltannealing ropertyffor an indelinite period of' time.A ty may-be' employed for holding lenses inany manner; :tor example, Whether the binder is applied to the lenses either singly or when the lenses are assembled, or to be assembled, ina block; whether or not the binder is brought to shape in a mold;

-Valso whether the binder is applied first to the lenses which are then attached to a holder, or nrst to the holder in the form of a layer to which the lenses are subsequently attached. The binder may be applied in the molten condition directly to the surface of the lens, or may be'initially formed into a pellet the surface of which is subsequently heated so as to'cause it 'to Vadhere to the lens to which it is applied. Before the application oi'i the binder, the lens may be warmed, and its surface may be coated with a sticky composition (known in the industry as tacky) whereby adhesion between the lens and binder is increased. The binder, if required to be molded, may be Vbrought to shape-in a mold whereotl one wall is constituted by the lens to which the binder is 5to be made to adhere, the mold being adapted to conine the binder within the area ot the lens; while distortion ot the lens be obviated by reducing the thickness of the molded mass of binder throughout a portion of its area, or byplacing a layer of non-adhesive material upon the center of the surface of the lens betere the binder is poured into the mold.

ln the accompanying drawings, Figures l and 2 illustrate, in side elevation and plan respectively, one form of'apparatus for heating and conditioning the binder, tor delivering it to lenses in molds, for closing the molds, and for coating the surface ot plication of the binder. Fig. 3 is a side elcvation partly in axial section, ol one of the moldsseen in Figs. l, d 2, (but drawn to a larger scale) together with the plunger `each lens withv tacky previous to the apwhich constitutes th-eclosure :for the mold;

a bi-conveX lens being shown in position in the mold. Fig. d is a partly sectional side view of a bi-convex 'lens with the molded mass vof binder adherent to it. Fig. 5y is a View similar to Fig. 4f, butshowing'a concave lens and means for preventingV adhe sion between the binder and the lens at the center of the latter. Fig. 6 is a side eleva tion cfa convenient form 'of ,tacky spraynozzle. f Y f 11 (Figs. l and 2) is'the hollowV body or container of a mixing machine, of well known type, which we'nd suitable for useV in heating and conditioning the binder, the

container being provided withVV a steam jacket 12vsupplied'rwithsteam throughV a pipe 13, while 14'is a pipe for draining' water of condensation from the Jacket. We

provide the container V1l with a removable cover land witha hopper 16 for the intra; Y

duction* of: fresh-binder intok the container,

the hopper being normally closed by a cover 17. l pair of rotary paddles 18, 18 mounted on shafts 19, 19 serve to stir up the binder Within the container 11; the shafts 19, 19 being geared together and adapted to be continuously driven by suitable means (not shown). A steam-jacketed pipe 2O leads from the interior of the container to the point Whereat the binder is to be delivered to the molds, this pipe terminating in an obliquely-cliamfered dependent nozzle 2l the passage between which and the pipe itself is controlled by a screw-down valve 22 'for regulating the rate oi delivery ot the binder.

By suitably adjusting the pressure of the steam Within the jacket l2, the binder Within the container 1l may be kept at the desired temperature ithout appreciable de terioration or loss of important volatile constituents, tlie conservation of which is assisted by the container beingl closed; While the continuous action of the paddles 18 serves to keep the mass of binder thoroughly homogeneous and uniform in temperature throughout.

The mold il.. shown in detail in Fig. 8 comprises base portion 23 surmounted by a circular ledge 2e presenting at its inner side a seating 25 of a diameter' to receive and hold the lens to which the binder is to be applied, the lens being supported around its margin only, While over the outer side of the ledge 24e is removably fitted an annular inwardly-conical cap 26 which, rising above the upper sur lace oi the lens. forms a coaming` adapted both to retain the lens in position Within the mold and also to connue the binder laterally during` the molding operation. The plunger B which terms the closure :for the mold is adapted to be brought into operative position, a'l'ter the mold has been illed with binder, by downward movement in. the direction of the common axis of the mold, lens and plunger', and, in the example illustrated, comprises an air nul ar rim 27 adapted to contact with the upper edge 42o ot the cap 26 and a central circular projection 29 which, by entering the mass ell binder bounded by the cap, forros in said mass a central depression 30, so that the binder 31 Which adheres to the lens 32 when the latter is removed from the mold presents in atrial section the profile shown in Fig. l.

ln order to facilitate the molding ot the binder upon a number oi' lenses in succes-- sion, a number oit molds A are detachably mounted upon a horizontal turntable 33 fitted to revolve about a fixed vertical stud 3&1. and provided at equal intervals with upright pegs B5 (Fig. 2) adapted to enter holes li/. (Fig. 3) in the base portions 23 of the several molds; the turntable 33 being rotated step-by-step through angular intershown in the drawing.

vals corresponding to those separating the pegs 85. For this purpose, in the example illustrated, the turntable 33 has on its lower side a dependent annular i'iange 37' in which are formed, al series of radial grooves 38 opening out at both the external and internal peripheries of the flange; these grooves, which are spacedapart at angular intervals correspending` to those bet-Ween the pegs 35, being engaged in succession by a pair ol crank pins 39 (carrying antitriction rollers) which project vertically from a disk e() fast ou the upper end of a vertical. shaft lll revolved at a suitable speed byany convenient means (not shown). rihe shaft ell may be continuously driven through frictional gearing so as to permit ot' any convenient means (not shown) being employed for arresting the rotation of the turntable 33 periodically dur-` ing the intervals when successive molds are being dealt with.

As seen in plan, Fig. 2, the turntable 33 is to be understood as intended to be re volved contracloclnviseso as to bring suecessive molds lirst, under a spray-nozzle 42 for delivering tacky on to the upper surface of each lens 32 in its mold, secondly, under the nozzle 21 through which the binder is delivered, and thirdly under the plunger B which serves as a closure vlor all the molds in succession. The. tacky Y may be ejected by any convenient means, for

example by a pneumatically-operated device such as is commonly employed for spraying paint, varnish or the like.

rl'he plunger B, which is shown in Fig. l as detachably fixed on the lower end olf a vertical. spindle 43 so as to be changeable to suit different molds, is actuated by slidingthe spindle "lf3 througha stationary guide J1-,fl supported on a bracket il-5 erztcnulinnl from the iXed stud 34,- about whicu the turntable revolves; the upper end ol the spindle 43 being connected by a linlr lo to a handlever 47 fulcrumed at 4S to the bracket e5. The spindle 411-3 may be normally retained the raised positiomso as to holdtlie plunger B clear of the molds A, by means of coiled spring housed Within the guide del but not els the plunger is depressed by means of the lever t7 until. arrested by the rim 27 encounteriino` the edge 28 of the mold-cap 26, the surplus binder escapes over the edge Alfter the binder has set to the shape given to it by the mold and plunger, the plunger is raised and the lens 32 with its adherent mass ol? binder can be removed from the mold. rEhe cen tral depression or cavity formed in the mass of pitch, (see Fig. e) leaves only an annular rim 50 ot' pitch by Which alone in such case the lens is subsequently attached to the holder for grinding or polishing.

W'hile in describing the new method which constitutes the present invention, the compoum i sition of a binder which may advantageously be treated by the method has been stated by wayY of example, it should be clearly understood that the invention is by no means limited to treatment of the binder Vwhose composition has been-set `out by way .not at any point in the mass exceedthe temperature Yat which such change occurs, to retain the self-annealing property of the material, and successively iwithdrawing small quantities fromV the mass and applying them to the lenses to form backings upon the lenses.

2. The method of preparing lenses and the like for grinding and polishing, which consists in heatinga mass of cement-itious material consisting chieiiy of pitch, having the property of self-annealing when cold, to a temperature which will render itY uid, maintaining the mass in a fiuid condition in a closed vessel at a uniform temperature which. does not exceed the tempmatureV which will cause destructive changes in said pitch while continuously stirring the mass so as to cause even distribution of the heat throughout Vthemass and prevent segregation of the ,constituents of the material, so that the self-annealing property of the pitch is retained7 and .successively withdrawing small quantities Yfrom said mass and apply- 'ing them to the lenses'to form backings for the lenses.

3. The method` of preparing lenses and the like for grinding andl polishing, which consists in heating a mass of cementitiousV material consisting chiefly of pitch, having the property of self-annealing when cold, to a temperature which will render it fluid, maintaining the mass in a fluid condition in closed vessel ata uniform temperature of about V130O to 14:00 C., while continuously stirring the mass so as to cause evendistribution ofthe heat throughout the'mass and prevent segregation of the constituents of the material, so that the self-annealing property of the pitch is retained, and successively withdrawing small quantities from said mass and applying them to the lenses to form backings for the lenses. Y

a. A method of preparing a plurality of lenses for mounting inV block, which con-1 sists in bringing a mass of binding material into fluid condition by the application of heat, and maintaining the mass at a uniform temperature and uniform consistency while successively withdrawing small quantities fromV said mass and applying them to the lenses so as to form uniform backings for the lenses. Y

A method of preparing lenses and the like for mounting in block, which comprises bringing a mass of binding material into Huid condition by the application of heat,

maintaining the mass at a .uniform temperayture and of a uniform consistency while successively withdrawing small quantities from'the mass, and molding them upon the back'of the lenses.

V6. A method of preparinglenses and the like for grinding in block, comprising bringing a mass of pitch into fluid condition by heat, and maintaining Vsaid mass of a uniform consistency by maintainingit at a uniform temperature in a closed vessel `and continuously stirring it, While succes sively withdrawing small quantities from the mass and molding them upon the backs ofthe individual lenses.

yWILLIAM TAYLOR. VliltiihlCS WILLIAM PRESTON. 

